Nanocellulose-reinforced cellulose fibers

ABSTRACT

Nanocellulose-reinforced cellulose fibers can increase the strength of hardwood fibers or agricultural-residue cellulose fibers, to simulate the strength of softwood fibers in pulp or pulp products (including composites). In some variations, the invention provides a method of reinforcing cellulose fibers, comprising providing cellulose fibers derived from hardwoods, agricultural residues, or a combination thereof; providing a source of nanocellulose comprising cellulose nanofibrils and/or cellulose nanocrystals; and reinforcing the cellulose fibers with the nanocellulose to increase strength of the cellulose fibers. In some embodiments, the nanocellulose is obtained from fractionating biomass in the presence of an acid, a solvent for lignin, and water, to generate cellulose-rich solids and a liquid phase; and then mechanically refining the cellulose-rich solids to generate the nanocellulose.

PRIORITY DATA

This patent application is a divisional application of U.S. patentapplication Ser. No. 14/750,888, filed on Jun. 25, 2015, which claimspriority to U.S. Provisional Patent App. No. 62/017,665, filed on Jun.26, 2014, each of which is hereby incorporated by reference herein.

FIELD

The present invention generally relates to nanocellulose and relatedmaterials produced by fractionating lignocellulosic biomass and furtherprocessing the cellulose fraction.

BACKGROUND

Biomass refining (or biorefining) has become more prevalent in industry.Cellulose fibers and sugars, hemicellulose sugars, lignin, syngas, andderivatives of these intermediates are being utilized for chemical andfuel production. Indeed, we now are observing the commercialization ofintegrated biorefineries that are capable of processing incoming biomassmuch the same as petroleum refineries now process crude oil.Underutilized lignocellulosic biomass feedstocks have the potential tobe much cheaper than petroleum, on a carbon basis, as well as muchbetter from an environmental life-cycle standpoint.

Lignocellulosic biomass is the most abundant renewable material on theplanet and has long been recognized as a potential feedstock forproducing chemicals, fuels, and materials. Lignocellulosic biomassnormally comprises primarily cellulose, hemicellulose, and lignin.Cellulose and hemicellulose are natural polymers of sugars, and ligninis an aromatic/aliphatic hydrocarbon polymer reinforcing the entirebiomass network. Some forms of biomass (e.g., recycled materials) do notcontain hemicellulose.

Despite being the most available natural polymer on earth, it is onlyrecently that cellulose has gained prominence as a nanostructuredmaterial, in the form of nanocrystalline cellulose (NCC), nanofibrillarcellulose (NFC), and bacterial cellulose (BC). Nanocellulose is beingdeveloped for use in a wide variety of applications such as polymerreinforcement, anti-microbial films, biodegradable food packaging,printing papers, pigments and inks, paper and board packaging, barrierfilms, adhesives, biocomposites, wound healing, pharmaceuticals and drugdelivery, textiles, water-soluble polymers, construction materials,recyclable interior and structural components for the transportationindustry, rheology modifiers, low-calorie food additives, cosmeticsthickeners, pharmaceutical tablet binders, bioactive paper, pickeringstabilizers for emulsion and particle stabilized foams, paintformulations, films for optical switching, and detergents. Despite themajor advantages of nanocellulose such as its non-toxicity and greatmechanical properties, its use to now has been in niche applications.Its moisture sensitivity, its incompatibility with oleophilic polymers,and the high energy consumption needed to produce, for example, NFC haveso far prevented it from competing with other mass products such asordinary paper or plastic. See “THE GLOBAL MARKET FOR NANOCELLULOSE TO2017,” FUTURE MARKETS INC. TECHNOLOGY REPORT No. 60, SECOND EDITION(October 2012).

Biomass-derived pulp may be converted to nanocellulose by mechanicalprocessing. Although the process may be simple, disadvantages includehigh energy consumption, damage to fibers and particles due to intensemechanical treatment, and a broad distribution in fibril diameter andlength.

Biomass-derived pulp may be converted to nanocellulose by chemicalprocessing. For example, pulp may be treated with2,2,6,6-tetramehylpiperidine-l-oxy radical (TEMPO) to producenanocellulose. Such a technique reduces energy consumption compared tomechanical treatment and can produce more uniform particle sizes, butthe process is not regarded as economically viable.

Improved processes for producing nanocellulose from biomass at reducedenergy costs are needed in the art. Also, improved starting materials(i.e., biomass-derived pulps) are needed in the art for producingnanocellulose. It would be particularly desirable for new processes topossess feedstock flexibility and process flexibility to produce eitheror both nanofibrils and nanocrystals, as well as to co-produce sugars,lignin, and other co-products. For some applications, it is desirable toproduce nanocellulose with high crystallinity, leading to goodmechanical properties of the nanocellulose or composites containing thenanocellulose. For certain applications, is would be beneficial toincrease the hydrophobicity of the nanocellulose.

There is also a need in the art for increasing the strength of weakcellulose fibers.

SUMMARY

In some variations, the present invention provides a method ofreinforcing cellulose fibers, the method comprising:

-   (a) providing cellulose fibers derived from hardwoods, agricultural    residues, or a combination thereof;-   (b) providing a source of nanocellulose comprising cellulose    nanofibrils and/or cellulose nanocrystals; and-   (c) reinforcing the cellulose fibers with the nanocellulose to    increase strength of the cellulose fibers.

In some embodiments, the nanocellulose is derived from a biomass sourceselected from the group consisting of hardwoods, softwoods, agriculturalresidues, and combinations thereof.

In some embodiments, the nanocellulose is obtained from fractionatingbiomass in the presence of an acid, a solvent for lignin, and water, togenerate cellulose-rich solids and a liquid phase; and then mechanicallyrefining the cellulose-rich solids to generate the nanocellulose. Incertain embodiments, the acid is sulfur dioxide and the solvent isethanol.

In some embodiments, the method further comprises producing asingle-fiber product from the cellulose fibers. In these or otherembodiments, the method further comprises producing a composite from thecellulose fibers.

Other variations of the invention provide a composition comprisingnanocellulose-reinforced hardwood cellulose fibers. Other variationsprovide a composition comprising nanocellulose-reinforcedagricultural-residue cellulose fibers. In some embodiments, thenanocellulose-reinforced cellulose fibers have higher strength than thecellulose fibers without the nanocellulose.

In some embodiments, the composition is produced by a method comprising:

-   (a) providing cellulose fibers derived from hardwoods, agricultural    residues, or a combination thereof;-   (b) providing a source of nanocellulose comprising cellulose    nanofibrils and/or cellulose nanocrystals; and-   (c) reinforcing the cellulose fibers with the nanocellulose to    increase strength of the cellulose fibers.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with any accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. All composition numbers and ranges based on percentages areweight percentages, unless indicated otherwise. All ranges of numbers orconditions are meant to encompass any specific value contained withinthe range, rounded to any suitable decimal point.

Unless otherwise indicated, all numbers expressing parameters, reactionconditions, concentrations of components, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending at least upon a specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

Generally it is beneficial to process biomass in a way that effectivelyseparates the major fractions (cellulose, hemicellulose, and lignin)from each other. The cellulose can be subjected to further processing toproduce nanocellulose. Fractionation of lignocellulosics leads torelease of cellulosic fibers and opens the cell wall structure bydissolution of lignin and hemicellulose between the cellulosemicrofibrils. The fibers become more accessible for conversion tonanofibrils or nanocrystals. Hemicellulose sugars can be fermented to avariety of products, such as ethanol, or converted to other chemicals.Lignin from biomass has value as a solid fuel and also as an energyfeedstock to produce liquid fuels, synthesis gas, or hydrogen; and as anintermediate to make a variety of polymeric compounds. Additionally,minor components such as proteins or rare sugars can be extracted andpurified for specialty applications.

This disclosure describes processes and apparatus to efficientlyfractionate any lignocellulosic-based biomass into its primary majorcomponents (cellulose, lignin, and if present, hemicellulose) so thateach can be used in potentially distinct processes. An advantage of theprocess is that it produces cellulose-rich solids while concurrentlyproducing a liquid phase containing a high yield of both hemicellulosesugars and lignin, and low quantities of lignin and hemicellulosedegradation products. The flexible fractionation technique enablesmultiple uses for the products. The cellulose is an advantaged precursorfor producing nanocellulose, as will be described herein.

The present invention, in some variations, utilizes the discovery thatnanocellulose and related materials can be produced under certainconditions including process conditions and steps associated with theAVAP® process. It has been found, surprisingly, that very highcrystallinity can be produced and maintained during formation ofnanofibers or nanocrystals, without the need for an enzymatic orseparate acid treatment step to hydrolyze amorphous cellulose. Highcrystallinity can translate to mechanically strong fibers or goodphysical reinforcing properties, which are advantageous for composites,reinforced polymers, and high-strength spun fibers and textiles, forexample.

A significant techno-economic barrier for production of cellulosenanofibrils (CNF) is high energy consumption and high cost. Using sulfurdioxide (SO₂) and ethanol (or other solvent), the pretreatment disclosedherein effectively removes not only hemicelluloses and lignin frombiomass but also the amorphous regions of cellulose, giving a unique,highly crystalline cellulose product that requires minimal mechanicalenergy for conversion to CNF. The low mechanical energy requirementresults from the fibrillated cellulose network formed during chemicalpretreatment upon removal of the amorphous regions of cellulose.

As intended herein, “nanocellulose” is broadly defined to include arange of cellulosic materials, including but not limited tomicrofibrillated cellulose, nanofibrillated cellulose, microcrystallinecellulose, nanocrystalline cellulose, and particulated or fibrillateddissolving pulp. Typically, nanocellulose as provided herein willinclude particles having at least one length dimension (e.g., diameter)on the nanometer scale.

“Nanofibrillated cellulose” or equivalently “cellulose nanofibrils”means cellulose fibers or regions that contain nanometer-sized particlesor fibers, or both micron-sized and nanometer-sized particles or fibers.“Nanocrystalline cellulose” or equivalently “cellulose nanocrystals”means cellulose particles, regions, or crystals that containnanometer-sized domains, or both micron-sized and nanometer-sizeddomains. “Micron-sized” includes from 1 to 100 μm and “nanometer-sized”includes from 0.01 nm to 1000 nm (1 μm). Larger domains (including longfibers) may also be present in these materials.

Certain exemplary embodiments of the invention will now be described.These embodiments are not intended to limit the scope of the inventionas claimed. The order of steps may be varied, some steps may be omitted,and/or other steps may be added. Reference herein to first step, secondstep, etc. is for purposes of illustrating some embodiments only.

In some variations, the present invention provides a method ofreinforcing cellulose fibers, the method comprising:

-   (a) providing cellulose fibers derived from hardwoods, agricultural    residues, or a combination thereof;-   (b) providing a source of nanocellulose comprising cellulose    nanofibrils and/or cellulose nanocrystals; and-   (c) reinforcing the cellulose fibers with the nanocellulose to    increase strength of the cellulose fibers.

In some embodiments, the nanocellulose is derived from a biomass sourceselected from the group consisting of hardwoods, softwoods, agriculturalresidues, and combinations thereof.

In some embodiments, the nanocellulose is obtained from fractionatingbiomass in the presence of an acid, a solvent for lignin, and water, togenerate cellulose-rich solids and a liquid phase; and then mechanicallyrefining the cellulose-rich solids to generate the nanocellulose. Incertain embodiments, the acid is sulfur dioxide and the solvent isethanol. In certain embodiments, an AVAP® process is used to makepreferred nanocellulose for reinforcing cellulose fibers.

“Reinforcing” can be accomplished by simple mixing, grinding, milling,agitation, or other treatments, in various embodiments.

In some embodiments, the method further comprises producing asingle-fiber product from the cellulose fibers. In these or otherembodiments, the method further comprises producing a composite from thecellulose fibers. Reinforcement of weak fibers with nanocellulose cansimulate the softwood-derived strength in composite and single fiberproducts, and other products.

In some embodiments, a product is made first from cellulose fibers, andthen the product (not the pulp) is reinforced with nanocellulose. Inthese embodiments, if desired, the reinforcement can be made to the bulkproduct or to selected surfaces or regions, for example.

Other variations of the invention provide a composition comprisingnanocellulose-reinforced hardwood cellulose fibers. Other variationsprovide a composition comprising nanocellulose-reinforcedagricultural-residue cellulose fibers. In some embodiments, thenanocellulose-reinforced cellulose fibers have higher strength than thecellulose fibers without the nanocellulose. For example, weak hardwoodfibers or agricultural-residue fibers may be made stronger, to simulatethe strength properties of softwood fibers, by reinforcing withnanocellulose.

In some embodiments, the composition is produced by a method comprising:

-   (a) providing cellulose fibers derived from hardwoods, agricultural    residues, or a combination thereof;-   (b) providing a source of nanocellulose comprising cellulose    nanofibrils and/or cellulose nanocrystals; and-   (c) reinforcing the cellulose fibers with the nanocellulose to    increase strength of the cellulose fibers.

In some variations, a process for producing a nanocellulose materialcomprises:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity (i.e., cellulose    crystallinity) of at least 60%; and-   (d) recovering the nanocellulose material.

In some embodiments, the acid is selected from the group consisting ofsulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid,lignosulfonic acid, and combinations thereof. In particular embodiments,the acid is sulfur dioxide.

The biomass feedstock may be selected from hardwoods, softwoods, forestresidues, eucalyptus, industrial wastes, pulp and paper wastes, consumerwastes, or combinations thereof. Some embodiments utilize agriculturalresidues, which include lignocellulosic biomass associated with foodcrops, annual grasses, energy crops, or other annually renewablefeedstocks. Exemplary agricultural residues include, but are not limitedto, corn stover, corn fiber, wheat straw, sugarcane bagasse, sugarcanestraw, rice straw, oat straw, barley straw, miscanthus, energy canestraw/residue, or combinations thereof. The process disclosed hereinbenefits from feedstock flexibility; it is effective for a wide varietyof cellulose-containing feedstocks.

As used herein, “lignocellulosic biomass” means any material containingcellulose and lignin. Lignocellulosic biomass may also containhemicellulose. Mixtures of one or more types of biomass can be used. Insome embodiments, the biomass feedstock comprises both a lignocellulosiccomponent (such as one described above) in addition to asucrose-containing component (e.g., sugarcane or energy cane) and/or astarch component (e.g., corn, wheat, rice, etc.). Various moisturelevels may be associated with the starting biomass. The biomassfeedstock need not be, but may be, relatively dry. In general, thebiomass is in the form of a particulate or chip, but particle size isnot critical in this invention.

In some embodiments, during step (c), the cellulose-rich solids aretreated with a total mechanical energy of less than about 1000kilowatt-hours per ton of the cellulose-rich solids, such as less thanabout 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350,300, or 250 kilowatt-hours per ton of the cellulose-rich solids. Incertain embodiments, the total mechanical energy is from about 100kilowatt-hours to about 400 kilowatt-hours per ton of the cellulose-richsolids. Energy consumption may be measured in any other suitable units.An ammeter measuring current drawn by a motor driving the mechanicaltreatment device is one way to obtain an estimate of the totalmechanical energy.

Mechanically treating in step (c) may employ one or more knowntechniques such as, but by no means limited to, milling, grinding,beating, sonicating, or any other means to form or release nanofibrilsand/or nanocrystals in the cellulose. Essentially, any type of mill ordevice that physically separates fibers may be utilized. Such mills arewell-known in the industry and include, without limitation, Valleybeaters, single disk refiners, double disk refiners, conical refiners,including both wide angle and narrow angle, cylindrical refiners,homogenizers, microfluidizers, and other similar milling or grindingapparatus. See, for example, Smook, Handbook for Pulp & PaperTechnologists, Tappi Press, 1992; and Hubbe et al., “CelluloseNanocomposites: A Review,” BioResources 3(3), 929-980 (2008).

The extent of mechanical treatment may be monitored during the processby any of several means. Certain optical instruments can providecontinuous data relating to the fiber length distributions and % fines,either of which may be used to define endpoints for the mechanicaltreatment step. The time, temperature, and pressure may vary duringmechanical treatment. For example, in some embodiments, sonication for atime from about 5 minutes to 2 hours, at ambient temperature andpressure, may be utilized.

In some embodiments, a portion of the cellulose-rich solids is convertedto nanofibrils while the remainder of the cellulose-rich solids is notfibrillated. In various embodiments, about 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, 95%, 99%, or substantially all of the cellulose-richsolids are fibrillated into nanofibrils.

In some embodiments, a portion of the nanofibrils is converted tonanocrystals while the remainder of the nanofibrils is not converted tonanocrystals. In various embodiments, about 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, 90%, 95%, 99%, or substantially all of the nanofibrilsare converted to nanocrystals. During drying, it is possible for a smallamount of nanocrystals to come back together and form nanofibrils.

Following mechanical treatment, the nanocellulose material may beclassified by particle size. A portion of material may be subjected to aseparate process, such as enzymatic hydrolysis to produce glucose. Suchmaterial may have good crystallinity, for example, but may not havedesirable particle size or degree of polymerization.

Step (c) may further comprise treatment of the cellulose-rich solidswith one or more enzymes or with one or more acids. When acids areemployed, they may be selected from the group consisting of sulfurdioxide, sulfurous acid, lignosulfonic acid, acetic acid, formic acid,and combinations thereof. Acids associated with hemicellulose, such asacetic acid or uronic acids, may be employed, alone or in conjunctionwith other acids. Also, step (c) may include treatment of thecellulose-rich solids with heat. In some embodiments, step (c) does notemploy any enzymes or acids.

In step (c), when an acid is employed, the acid may be a strong acidsuch as sulfuric acid, nitric acid, or phosphoric acid, for example.Weaker acids may be employed, under more severe temperature and/or time.Enzymes that hydrolyze cellulose (i.e., cellulases) and possiblyhemicellulose (i.e., with hemicellulase activity) may be employed instep (c), either instead of acids, or potentially in a sequentialconfiguration before or after acidic hydrolysis.

In some embodiments, the process comprises enzymatically treating thecellulose-rich solids to hydrolyze amorphous cellulose. In otherembodiments, or sequentially prior to or after enzymatic treatment, theprocess may comprise acid-treating the cellulose-rich solids tohydrolyze amorphous cellulose.

In some embodiments, the process further comprises enzymaticallytreating the nanocrystalline cellulose. In other embodiments, orsequentially prior to or after enzymatic treatment, the process furthercomprises acid-treating treating the nanocrystalline cellulose.

If desired, an enzymatic treatment may be employed prior to, or possiblysimultaneously with, the mechanical treatment. However, in preferredembodiments, no enzyme treatment is necessary to hydrolyze amorphouscellulose or weaken the structure of the fiber walls before isolation ofnanofibers.

Following mechanical treatment, the nanocellulose may be recovered.Separation of cellulose nanofibrils and/or nanocrystals may beaccomplished using apparatus capable of disintegrating theultrastructure of the cell wall while preserving the integrity of thenanofibrils. For example, a homogenizer may be employed. In someembodiments, cellulose aggregate fibrils are recovered, having componentfibrils in range of 1-100 nm width, wherein the fibrils have not beencompletely separated from each other.

The process may further comprise bleaching the cellulose-rich solidsprior to step (c) and/or as part of step (c). Alternatively, oradditionally, the process may further comprise bleaching thenanocellulose material during step (c) and/or following step (c). Anyknown bleaching technology or sequence may be employed, includingenzymatic bleaching.

The nanocellulose material may include, or consist essentially of,nanofibrillated cellulose. The nanocellulose material may include, orconsist essentially of, nanocrystalline cellulose. In some embodiments,the nanocellulose material may include, or consist essentially of,nanofibrillated cellulose and nanocrystalline cellulose.

In some embodiments, the crystallinity of the cellulose-rich solids(i.e., the nanocellulose precursor material) is at least 60%, 61%, 62%,63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%,77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86% or higher. In these orother embodiments, the crystallinity of the nanocellulose material is atleast 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%,73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86% orhigher. The crystallinity may be measured using any known techniques.For example, X-ray diffraction and solid-state ¹³C nuclear magneticresonance may be utilized.

It is remarkable that the nanocellulose precursor material has highcrystallinity—which generally contributes to mechanical strength—yet,very low mechanical energy consumption is necessary to break apart thenanocellulose precursor material into nanofibrils and nanocrystals. Itis believed that since the mechanical energy input is low, the highcrystallinity is essentially maintained in the final product.

In some embodiments, the nanocellulose material is characterized by anaverage degree of polymerization from about 100 to about 1500, such asabout 125, 150, 175, 200, 225, 250, 300, 400, 500, 600, 700, 800, 900,1000, 1100, 1200, 1300, or 1400. For example, the nanocellulose materialmay be characterized by an average degree of polymerization from about300 to about 700, or from about 150 to about 250. The nanocellulosematerial, when in the form of nanocrystals, may have a degree ofpolymerization less than 100, such as about 75, 50, 25, or 10. Portionsof the material may have a degree of polymerization that is higher than1500, such as about 2000, 3000, 4000, or 5000.

In some embodiments, the nanocellulose material is characterized by adegree of polymerization distribution having a single peak. In otherembodiments, the nanocellulose material is characterized by a degree ofpolymerization distribution having two peaks, such as one centered inthe range of 150-250 and another peak centered in the range of 300-700.

In some embodiments, the nanocellulose material is characterized by anaverage length-to-width aspect ratio of particles from about 10 to about1000, such as about 15, 20, 25, 35, 50, 75, 100, 150, 200, 250, 300,400, or 500. Nanofibrils are generally associated with higher aspectratios than nanocrystals. Nanocrystals, for example, may have a lengthrange of about 100 nm to 500 nm and a diameter of about 4 nm,translating to an aspect ratio of 25 to 125. Nanofibrils may have alength of about 2000 nm and diameter range of 5 to 50 nm, translating toan aspect ratio of 40 to 400. In some embodiments, the aspect ratio isless than 50, less than 45, less than 40, less than 35, less than 30,less than 25, less than 20, less than 15, or less than 10.

Optionally, the process further comprises hydrolyzing amorphouscellulose into glucose in step (b) and/or step (c), recovering theglucose, and fermenting the glucose to a fermentation product.Optionally, the process further comprises recovering, fermenting, orfurther treating hemicellulosic sugars derived from the hemicellulose.Optionally, the process further comprises recovering, combusting, orfurther treating the lignin.

Glucose that is generated from hydrolysis of amorphous cellulose may beintegrated into an overall process to produce ethanol, or anotherfermentation co-product. Thus in some embodiments, the process furthercomprises hydrolyzing amorphous cellulose into glucose in step (b)and/or step (c), and recovering the glucose. The glucose may be purifiedand sold. Or the glucose may be fermented to a fermentation product,such as but not limited to ethanol. The glucose or a fermentationproduct may be recycled to the front end, such as to hemicellulose sugarprocessing, if desired.

When hemicellulosic sugars are recovered and fermented, they may befermented to produce a monomer or precursor thereof. The monomer may bepolymerized to produce a polymer, which may then be combined with thenanocellulose material to form a polymer-nanocellulose composite.

In some embodiments, the nanocellulose material is at least partiallyhydrophobic via deposition of at least some of the lignin onto a surfaceof the cellulose-rich solids during step (b). In these or otherembodiments, the nanocellulose material is at least partiallyhydrophobic via deposition of at least some of the lignin onto a surfaceof the nanocellulose material during step (c) or step (d).

In some embodiments, the process further comprises chemically convertingthe nanocellulose material to one or more nanocellulose derivatives. Forexample, nanocellulose derivatives may be selected from the groupconsisting of nanocellulose esters, nanocellulose ethers, nanocelluloseether esters, alkylated nanocellulose compounds, cross-linkednanocellulose compounds, acid-functionalized nanocellulose compounds,base-functionalized nanocellulose compounds, and combinations thereof.

Various types of nanocellulose functionalization or derivatization maybe employed, such as functionalization using polymers, chemical surfacemodification, functionalization using nanoparticles (i.e. othernanoparticles besides the nanocellulose), modification with inorganicsor surfactants, or biochemical modification.

Certain variations provide a process for producing a nanocellulosematerial, the process comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of sulfur dioxide, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose oligomers and lignin, wherein the    crystallinity of the cellulose-rich solids is at least 70%, wherein    SO₂ concentration is from about 10 wt % to about 50 wt %,    fractionation temperature is from about 130° C. to about 200° C.,    and fractionation time is from about 30 minutes to about 4 hours;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 70%; and-   (d) recovering the nanocellulose material.

In some embodiments, the SO2 concentration is from about 12 wt % toabout 30 wt %. In some embodiments, the fractionation temperature isfrom about 140° C. to about 170° C. In some embodiments, thefractionation time is from about 1 hour to about 2 hours. The processmay be controlled such that during step (b), a portion of thesolubilized lignin intentionally deposits back onto a surface of thecellulose-rich solids, thereby rendering the cellulose-rich solids atleast partially hydrophobic.

A significant factor limiting the application of strength-enhancing,lightweight nanocellulose in composites is cellulose's inherenthydrophilicity. Surface modification of the nanocellulose surface toimpart hydrophobicity to enable uniform dispersion in a hydrophobicpolymer matrix is an active area of study. It has been discovered thatwhen preparing nanocellulose using the processes described herein,lignin may condense on pulp under certain conditions, giving a rise inKappa number and production of a brown or black material. The ligninincreases the hydrophobicity of the nanocellulose precursor material,and that hydrophobicity is retained during mechanical treatment providedthat there is not removal of the lignin through bleaching or othersteps. (Some bleaching may still be performed, either to adjust lignincontent or to attack a certain type of lignin, for example.)

In some embodiments, the present invention provides a process forproducing a hydrophobic nanocellulose material, the process comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin, wherein a portion of    the lignin deposits onto a surface of the cellulose-rich solids,    thereby rendering the cellulose-rich solids at least partially    hydrophobic;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    hydrophobic nanocellulose material having a crystallinity of at    least 60%; and-   (d) recovering the hydrophobic nanocellulose material.

In some embodiments, the acid is selected from the group consisting ofsulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid,lignosulfonic acid, and combinations thereof.

In some embodiments, during step (c), the cellulose-rich solids aretreated with a total mechanical energy of less than about 1000kilowatt-hours per ton of the cellulose-rich solids, such as less thanabout 500 kilowatt-hours per ton of the cellulose-rich solids.

The crystallinity of the nanocellulose material is at least 70% or atleast 80%, in various embodiments.

The nanocellulose material may include nanofibrillated cellulose,nanocrystalline cellulose, or both nanofibrillated and nanocrystallinecellulose. The nanocellulose material may be characterized by an averagedegree of polymerization from about 100 to about 1500, such as fromabout 300 to about 700, or from about 150 to about 250, for example(without limitation).

Step (b) may include process conditions, such as extended time and/ortemperature, or reduced concentration of solvent for lignin, which tendto promote lignin deposition onto fibers. Alternatively, oradditionally, step (b) may include one or more washing steps that areadapted to deposit at least some of the lignin that was solubilizedduring the initial fractionation. One approach is to wash with waterrather than a solution of water and solvent. Because lignin is generallynot soluble in water, it will begin to precipitate. Optionally, otherconditions may be varied, such as pH and temperature, duringfractionation, washing, or other steps, to optimize the amount of lignindeposited on surfaces. It is noted that in order for the lignin surfaceconcentration to be higher than the bulk concentration, the lignin needsto be first pulled into solution and then redeposited; internal lignin(within particles of nanocellulose) does not enhance hydrophobicity inthe same way.

Optionally, the process for producing a hydrophobic nanocellulosematerial may further include chemically modifying the lignin to increasehydrophobicity of the nanocellulose material. The chemical modificationof lignin may be conducted during step (b), step (c), step (d),following step (d), or some combination.

High loading rates of lignin have been achieved in thermoplastics. Evenhigher loading levels are obtained with well-known modifications oflignin. The preparation of useful polymeric materials containing asubstantial amount of lignin has been the subject of investigations formore than thirty years. Typically, lignin may be blended intopolyolefins or polyesters by extrusion up to 25-40 wt % while satisfyingmechanical characteristics. In order to increase the compatibilitybetween lignin and other hydrophobic polymers, different approaches havebeen used. For example, chemical modification of lignin may beaccomplished through esterification with long-chain fatty acids.

Any known chemical modifications may be carried out on the lignin, tofurther increase the hydrophobic nature of the lignin-coatednanocellulose material provided by embodiments of this invention.

The present invention also provides, in some variations, a process forproducing a nanocellulose-containing product, the process comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 60%; and-   (d) incorporating at least a portion of the nanocellulose material    into a nanocellulose-containing product.

The nanocellulose-containing product includes the nanocellulosematerial, or a treated form thereof In some embodiments, thenanocellulose-containing product consists essentially of thenanocellulose material.

In some embodiments, step (d) comprises forming a structural object thatincludes the nanocellulose material, or a derivative thereof.

In some embodiments, step (d) comprises forming a foam or aerogel thatincludes the nanocellulose material, or a derivative thereof.

In some embodiments, step (d) comprises combining the nanocellulosematerial, or a derivative thereof, with one or more other materials toform a composite. For example, the other material may include a polymerselected from polyolefins, polyesters, polyurethanes, polyamides, orcombinations thereof. Alternatively, or additionally, the other materialmay include carbon in various forms.

The nanocellulose material incorporated into a nanocellulose-containingproduct may be at least partially hydrophobic via deposition of at leastsome of the lignin onto a surface of the cellulose-rich solids duringstep (b). Also, the nanocellulose material may be at least partiallyhydrophobic via deposition of at least some of the lignin onto a surfaceof the nanocellulose material during step (c) or step (d).

In some embodiments, step (d) comprises forming a film comprising thenanocellulose material, or a derivative thereof. The film is opticallytransparent and flexible, in certain embodiments.

In some embodiments, step (d) comprises forming a coating or coatingprecursor comprising the nanocellulose material, or a derivative thereofIn some embodiments, the nanocellulose-containing product is a papercoating.

In some embodiments, the nanocellulose-containing product is configuredas a catalyst, catalyst substrate, or co-catalyst. In some embodiments,the nanocellulose-containing product is configured electrochemically forcarrying or storing an electrical current or voltage.

In some embodiments, the nanocellulose-containing product isincorporated into a filter, membrane, or other separation device.

In some embodiments, the nanocellulose-containing product isincorporated as an additive into a coating, paint, or adhesive. In someembodiments, the nanocellulose-containing product is incorporated as acement additive.

In some embodiments, the nanocellulose-containing product isincorporated as a thickening agent or rheological modifier. For example,the nanocellulose-containing product may be an additive in a drillingfluid, such as (but not limited to) an oil recovery fluid and/or a gasrecovery fluid.

The present invention also provides nanocellulose compositions. In somevariations, a nanocellulose composition comprises nanofibrillatedcellulose with a cellulose crystallinity of about 70% or greater. Thenanocellulose composition may include lignin and sulfur.

The nanocellulose material may further contain some sulfonated ligninthat is derived from sulfonation reactions with SO2 (when used as theacid in fractionation) during the biomass digestion. The amount ofsulfonated lignin may be about 0.1 wt % (or less), 0.2 wt %, 0.5 wt %,0.8 wt %, 1 wt %, or more. Also, without being limited by any theory, itis speculated that a small amount of sulfur may chemically react withcellulose itself, in some embodiments.

In some variations, a nanocellulose composition comprisesnanofibrillated cellulose and nanocrystalline cellulose, wherein thenanocellulose composition is characterized by an overall cellulosecrystallinity of about 70% or greater. The nanocellulose composition mayinclude lignin and sulfur.

In some variations, a nanocellulose composition comprisesnanocrystalline cellulose with a cellulose crystallinity of about 80% orgreater, wherein the nanocellulose composition comprises lignin andsulfur.

In some embodiments, the cellulose crystallinity is about 75% orgreater, such as about 80% or greater, or about 85% or greater. Invarious embodiments, the nanocellulose composition is not derived fromtunicates.

The nanocellulose composition of some embodiments is characterized by anaverage cellulose degree of polymerization from about 100 to about 1000,such as from about 300 to about 700 or from about 150 to about 250. Incertain embodiments, the nanocellulose composition is characterized by acellulose degree of polymerization distribution having a single peak. Incertain embodiments, the nanocellulose composition is free of enzymes.

Other variations provide a hydrophobic nanocellulose composition with acellulose crystallinity of about 70% or greater, wherein thenanocellulose composition contains nanocellulose particles having asurface concentration of lignin that is greater than a bulk (internalparticle) concentration of lignin. In some embodiments, there is acoating or thin film of lignin on nanocellulose particles, but thecoating or film need not be uniform.

The hydrophobic nanocellulose composition may have a cellulosecrystallinity is about 75% or greater, about 80% or greater, or about85% or greater. The hydrophobic nanocellulose composition may furtherinclude sulfur.

The hydrophobic nanocellulose composition may or may not be derived fromtunicates. The hydrophobic nanocellulose composition may be free ofenzymes.

In some embodiments, the hydrophobic nanocellulose composition ischaracterized by an average cellulose degree of polymerization fromabout 100 to about 1500, such as from about 300 to about 700 or fromabout 150 to about 250. The nanocellulose composition may becharacterized by a cellulose degree of polymerization distributionhaving a single peak.

A nanocellulose-containing product may include any of the disclosednanocellulose compositions. Many nanocellulose-containing products arepossible. For example, a nanocellulose-containing product may beselected from the group consisting of a structural object, a foam, anaerogel, a polymer composite, a carbon composite, a film, a coating, acoating precursor, a current or voltage carrier, a filter, a membrane, acatalyst, a catalyst substrate, a coating additive, a paint additive, anadhesive additive, a cement additive, a paper coating, a thickeningagent, a rheological modifier, an additive for a drilling fluid, andcombinations or derivatives thereof

Some variations provide a nanocellulose material produced by a processcomprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 60%; and-   (d) recovering the nanocellulose material.

Some embodiments provide a polymer-nanocellulose composite materialproduced by a process comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 60%;-   (d) recovering the nanocellulose material;-   (e) fermenting hemicellulosic sugars derived from the hemicellulose    to produce a monomer or precursor thereof-   (f) polymerizing the monomer to produce a polymer; and-   (g) combining the polymer and the nanocellulose material to form the    polymer-nanocellulose composite.

Some variations provide a nanocellulose material produced by a processcomprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of sulfur dioxide, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose oligomers and lignin, wherein the    crystallinity of the cellulose-rich solids is at least 70%, wherein    SO₂ concentration is from about 10 wt % to about 50 wt %,    fractionation temperature is from about 130° C. to about 200° C.,    and fractionation time is from about 30 minutes to about 4 hours;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 70%; and-   (d) recovering the nanocellulose material.

Some variations provide a hydrophobic nanocellulose material produced bya process comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin, wherein a portion of    the lignin deposits onto a surface of the cellulose-rich solids,    thereby rendering the cellulose-rich solids at least partially    hydrophobic;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    hydrophobic nanocellulose material having a crystallinity of at    least 60%; and-   (d) recovering the hydrophobic nanocellulose material.

Some variations provide a nanocellulose-containing product produced by aprocess comprising:

-   (a) providing a lignocellulosic biomass feedstock;-   (b) fractionating the feedstock in the presence of an acid, a    solvent for lignin, and water, to generate cellulose-rich solids and    a liquid containing hemicellulose and lignin;-   (c) mechanically treating the cellulose-rich solids to form    cellulose fibrils and/or cellulose crystals, thereby generating a    nanocellulose material having a crystallinity of at least 60%; and-   (d) incorporating at least a portion of the nanocellulose material    into a nanocellulose-containing product.

A nanocellulose-containing product that contains the nanocellulosematerial may be selected from the group consisting of a structuralobject, a foam, an aerogel, a polymer composite, a carbon composite, afilm, a coating, a coating precursor, a current or voltage carrier, afilter, a membrane, a catalyst, a catalyst substrate, a coatingadditive, a paint additive, an adhesive additive, a cement additive, apaper coating, a thickening agent, a rheological modifier, an additivefor a drilling fluid, and combinations or derivatives thereof.

Various embodiments will now be further described, without limitation asto the scope of the invention. These embodiments are exemplary innature.

In some embodiments, a first process step is “cooking” (equivalently,“digesting”) which fractionates the three lignocellulosic materialcomponents (cellulose, hemicellulose, and lignin) to allow easydownstream removal. Specifically, hemicelluloses are dissolved and over50% are completely hydrolyzed; cellulose is separated but remainsresistant to hydrolysis; and part of the lignin is sulfonated intowater-soluble lignosulfonates.

The lignocellulosic material is processed in a solution (cooking liquor)of aliphatic alcohol, water, and sulfur dioxide. The cooking liquorpreferably contains at least 10 wt %, such as at least 20 wt %, 30 wt %,40 wt %, or 50 wt % of a solvent for lignin. For example, the cookingliquor may contain about 30-70 wt % solvent, such as about 50 wt %solvent. The solvent for lignin may be an aliphatic alcohol, such asmethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,isobutanol, 1-pentanol, 1-hexanol, or cyclohexanol. The solvent forlignin may be an aromatic alcohol, such as phenol or cresol. Otherlignin solvents are possible, such as (but not limited to) glycerol,methyl ethyl ketone, or diethyl ether. Combinations of more than onesolvent may be employed.

Preferably, enough solvent is included in the extractant mixture todissolve the lignin present in the starting material. The solvent forlignin may be completely miscible, partially miscible, or immisciblewith water, so that there may be more than one liquid phase. Potentialprocess advantages arise when the solvent is miscible with water, andalso when the solvent is immiscible with water. When the solvent iswater-miscible, a single liquid phase forms, so mass transfer of ligninand hemicellulose extraction is enhanced, and the downstream processmust only deal with one liquid stream. When the solvent is immiscible inwater, the extractant mixture readily separates to form liquid phases,so a distinct separation step can be avoided or simplified. This can beadvantageous if one liquid phase contains most of the lignin and theother contains most of the hemicellulose sugars, as this facilitatesrecovering the lignin from the hemicellulose sugars.

The cooking liquor preferably contains sulfur dioxide and/or sulfurousacid (H₂SO₃). The cooking liquor preferably contains SO₂, in dissolvedor reacted form, in a concentration of at least 3 wt %, preferably atleast 6 wt %, more preferably at least 8 wt %, such as about 9 wt %, 10wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt %, 15 wt %, 20 wt %, 25 wt %, 30wt % or higher. The cooking liquor may also contain one or more species,separately from SO₂, to adjust the pH. The pH of the cooking liquor istypically about 4 or less.

Sulfur dioxide is a preferred acid catalyst, because it can be recoveredeasily from solution after hydrolysis. The majority of the SO₂ from thehydrolysate may be stripped and recycled back to the reactor. Recoveryand recycling translates to less lime required compared toneutralization of comparable sulfuric acid, less solids to dispose of,and less separation equipment. The increased efficiency owing to theinherent properties of sulfur dioxide mean that less total acid or othercatalysts may be required. This has cost advantages, since sulfuric acidcan be expensive. Additionally, and quite significantly, less acid usagealso will translate into lower costs for a base (e.g., lime) to increasethe pH following hydrolysis, for downstream operations. Furthermore,less acid and less base will also mean substantially less generation ofwaste salts (e.g., gypsum) that may otherwise require disposal.

In some embodiments, an additive may be included in amounts of about 0.1wt % to 10 wt % or more to increase cellulose viscosity. Exemplaryadditives include ammonia, ammonia hydroxide, urea, anthraquinone,magnesium oxide, magnesium hydroxide, sodium hydroxide, and theirderivatives.

The cooking is performed in one or more stages using batch or continuousdigestors. Solid and liquid may flow cocurrently or countercurrently, orin any other flow pattern that achieves the desired fractionation. Thecooking reactor may be internally agitated, if desired.

Depending on the lignocellulosic material to be processed, the cookingconditions are varied, with temperatures from about 65° C. to 190° C.,for example 75° C., 85° C., 95° C., 105° C., 115° C., 125° C., 130° C.,135° C., 140° C., 145° C., 150° C., 155° C., 165° C. or 170° C., andcorresponding pressures from about 1 atmosphere to about 15 atmospheresin the liquid or vapor phase. The cooking time of one or more stages maybe selected from about 15 minutes to about 720 minutes, such as about30, 45, 60, 90, 120, 140, 160, 180, 250, 300, 360, 450, 550, 600, or 700minutes. Generally, there is an inverse relationship between thetemperature used during the digestion step and the time needed to obtaingood fractionation of the biomass into its constituent parts.

The cooking liquor to lignocellulosic material ratio may be selectedfrom about 1 to about 10, such as about 2, 3, 4, 5, or 6. In someembodiments, biomass is digested in a pressurized vessel with low liquorvolume (low ratio of cooking liquor to lignocellulosic material), sothat the cooking space is filled with ethanol and sulfur dioxide vaporin equilibrium with moisture. The cooked biomass is washed inalcohol-rich solution to recover lignin and dissolved hemicelluloses,while the remaining pulp is further processed. In some embodiments, theprocess of fractionating lignocellulosic material comprises vapor-phasecooking of lignocellulosic material with aliphatic alcohol (or othersolvent for lignin), water, and sulfur dioxide. See, for example, U.S.Pat. Nos. 8,038,842 and 8,268,125 which are incorporated by referenceherein.

A portion or all of the sulfur dioxide may be present as sulfurous acidin the extract liquor. In certain embodiments, sulfur dioxide isgenerated in situ by introducing sulfurous acid, sulfite ions, bisulfiteions, combinations thereof, or a salt of any of the foregoing. Excesssulfur dioxide, following hydrolysis, may be recovered and reused.

In some embodiments, sulfur dioxide is saturated in water (or aqueoussolution, optionally with an alcohol) at a first temperature, and thehydrolysis is then carried out at a second, generally higher,temperature. In some embodiments, sulfur dioxide is sub-saturated. Insome embodiments, sulfur dioxide is super-saturated. In someembodiments, sulfur dioxide concentration is selected to achieve acertain degree of lignin sulfonation, such as 1%, 2%, 3%, 4%, 5%, 6%,7%, 8%, 9%, or 10% sulfur content. SO₂ reacts chemically with lignin toform stable lignosulfonic acids which may be present both in the solidand liquid phases.

The concentration of sulfur dioxide, additives, and aliphatic alcohol(or other solvent) in the solution and the time of cook may be varied tocontrol the yield of cellulose and hemicellulose in the pulp. Theconcentration of sulfur dioxide and the time of cook may be varied tocontrol the yield of lignin versus lignosulfonates in the hydrolysate.In some embodiments, the concentration of sulfur dioxide, temperature,and the time of cook may be varied to control the yield of fermentablesugars.

Once the desired amount of fractionation of both hemicellulose andlignin from the solid phase is achieved, the liquid and solid phases areseparated. Conditions for the separation may be selected to minimize orenhance the reprecipitation of the extracted lignin on the solid phase.Minimizing lignin reprecipitation is favored by conducting separation orwashing at a temperature of at least the glass-transition temperature oflignin (about 120° C.); conversely, enhancing lignin reprecipitation isfavored by conducting separation or washing at a temperature less thanthe glass-transition temperature of lignin.

The physical separation can be accomplished either by transferring theentire mixture to a device that can carry out the separation andwashing, or by removing only one of the phases from the reactor whilekeeping the other phase in place. The solid phase can be physicallyretained by appropriately sized screens through which liquid can pass.The solid is retained on the screens and can be kept there forsuccessive solid-wash cycles. Alternately, the liquid may be retainedand solid phase forced out of the reaction zone, with centrifugal orother forces that can effectively transfer the solids out of the slurry.In a continuous system, countercurrent flow of solids and liquid canaccomplish the physical separation.

The recovered solids normally will contain a quantity of lignin andsugars, some of which can be removed easily by washing. Thewashing-liquid composition can be the same as or different than theliquor composition used during fractionation. Multiple washes may beperformed to increase effectiveness. Preferably, one or more washes areperformed with a composition including a solvent for lignin, to removeadditional lignin from the solids, followed by one or more washes withwater to displace residual solvent and sugars from the solids. Recyclestreams, such as from solvent-recovery operations, may be used to washthe solids.

After separation and washing as described, a solid phase and at leastone liquid phase are obtained. The solid phase contains substantiallyundigested cellulose. A single liquid phase is usually obtained when thesolvent and the water are miscible in the relative proportions that arepresent. In that case, the liquid phase contains, in dissolved form,most of the lignin originally in the starting lignocellulosic material,as well as soluble monomeric and oligomeric sugars formed in thehydrolysis of any hemicellulose that may have been present. Multipleliquid phases tend to form when the solvent and water are wholly orpartially immiscible. The lignin tends to be contained in the liquidphase that contains most of the solvent. Hemicellulose hydrolysisproducts tend to be present in the liquid phase that contains most ofthe water.

In some embodiments, hydrolysate from the cooking step is subjected topressure reduction. Pressure reduction may be done at the end of a cookin a batch digestor, or in an external flash tank after extraction froma continuous digestor, for example. The flash vapor from the pressurereduction may be collected into a cooking liquor make-up vessel. Theflash vapor contains substantially all the unreacted sulfur dioxidewhich may be directly dissolved into new cooking liquor. The celluloseis then removed to be washed and further treated as desired.

A process washing step recovers the hydrolysate from the cellulose. Thewashed cellulose is pulp that may be used for various purposes (e.g.,paper or nanocellulose production). The weak hydrolysate from the washercontinues to the final reaction step; in a continuous digestor this weakhydrolysate may be combined with the extracted hydrolysate from theexternal flash tank. In some embodiments, washing and/or separation ofhydrolysate and cellulose-rich solids is conducted at a temperature ofat least about 100° C., 110° C., or 120° C. The washed cellulose mayalso be used for glucose production via cellulose hydrolysis withenzymes or acids.

In another reaction step, the hydrolysate may be further treated in oneor multiple steps to hydrolyze the oligomers into monomers. This stepmay be conducted before, during, or after the removal of solvent andsulfur dioxide. The solution may or may not contain residual solvent(e.g. alcohol). In some embodiments, sulfur dioxide is added or allowedto pass through to this step, to assist hydrolysis. In these or otherembodiments, an acid such as sulfurous acid or sulfuric acid isintroduced to assist with hydrolysis. In some embodiments, thehydrolysate is autohydrolyzed by heating under pressure. In someembodiments, no additional acid is introduced, but lignosulfonic acidsproduced during the initial cooking are effective to catalyze hydrolysisof hemicellulose oligomers to monomers. In various embodiments, thisstep utilizes sulfur dioxide, sulfurous acid, sulfuric acid at aconcentration of about 0.01 wt % to 30 wt %, such as about 0.05 wt %,0.1 wt %, 0.2 wt %, 0.5 wt %, 1 wt %, 2 wt %, 5 wt %, 10 wt %, or 20 wt%. This step may be carried out at a temperature from about 100° C. to220° C., such as about 110° C., 120° C., 130° C., 140° C., 150° C., 160°C., 170° C., 180° C., 190° C., 200° C., or 210° C. Heating may be director indirect to reach the selected temperature.

The reaction step produces fermentable sugars which can then beconcentrated by evaporation to a fermentation feedstock. Concentrationby evaporation may be accomplished before, during, or after thetreatment to hydrolyze oligomers. The final reaction step may optionallybe followed by steam stripping of the resulting hydrolysate to removeand recover sulfur dioxide and alcohol, and for removal of potentialfermentation-inhibiting side products. The evaporation process may beunder vacuum or pressure, from about −0.1 atmospheres to about 10atmospheres, such as about 0.1 atm, 0.3 atm, 0.5 atm, 1.0 atm, 1.5 atm,2 atm, 4 atm, 6 atm, or 8 atm.

Recovering and recycling the sulfur dioxide may utilize separations suchas, but not limited to, vapor-liquid disengagement (e.g. flashing),steam stripping, extraction, or combinations or multiple stages thereof.Various recycle ratios may be practiced, such as about 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or more. In some embodiments, about90-99% of initially charged SO₂ is readily recovered by distillationfrom the liquid phase, with the remaining 1-10% (e.g., about 3-5%) ofthe SO₂ primarily bound to dissolved lignin in the form oflignosulfonates.

In a preferred embodiment, the evaporation step utilizes an integratedalcohol stripper and evaporator. Evaporated vapor streams may besegregated so as to have different concentrations of organic compoundsin different streams. Evaporator condensate streams may be segregated soas to have different concentrations of organic compounds in differentstreams. Alcohol may be recovered from the evaporation process bycondensing the exhaust vapor and returning to the cooking liquor make-upvessel in the cooking step. Clean condensate from the evaporationprocess may be used in the washing step.

In some embodiments, an integrated alcohol stripper and evaporatorsystem is employed, wherein aliphatic alcohol is removed by vaporstripping, the resulting stripper product stream is concentrated byevaporating water from the stream, and evaporated vapor is compressedusing vapor compression and is reused to provide thermal energy.

The hydrolysate from the evaporation and final reaction step containsmainly fermentable sugars but may also contain lignin depending on thelocation of lignin separation in the overall process configuration. Thehydrolysate may be concentrated to a concentration of about 5 wt % toabout 60 wt % solids, such as about 10 wt %, 15 wt %, 20 wt %, 25 wt %,30 wt %, 35 wt %, 40 wt %, 45 wt %, 50 wt % or 55 wt % solids. Thehydrolysate contains fermentable sugars.

Fermentable sugars are defined as hydrolysis products of cellulose,galactoglucomannan, glucomannan, arabinoglucuronoxylans,arabinogalactan, and glucuronoxylans into their respective short-chainedoligomers and monomer products, i.e., glucose, mannose, galactose,xylose, and arabinose. The fermentable sugars may be recovered inpurified form, as a sugar slurry or dry sugar solids, for example. Anyknown technique may be employed to recover a slurry of sugars or to drythe solution to produce dry sugar solids.

In some embodiments, the fermentable sugars are fermented to producebiochemicals or biofuels such as (but by no means limited to) ethanol,isopropanol, acetone, 1-butanol, isobutanol, lactic acid, succinic acid,or any other fermentation products. Some amount of the fermentationproduct may be a microorganism or enzymes, which may be recovered ifdesired.

When the fermentation will employ bacteria, such as Clostridia bacteria,it is preferable to further process and condition the hydrolysate toraise pH and remove residual SO₂ and other fermentation inhibitors. Theresidual SO₂ (i.e., following removal of most of it by stripping) may becatalytically oxidized to convert residual sulfite ions to sulfate ionsby oxidation. This oxidation may be accomplished by adding an oxidationcatalyst, such as FeSO4.7H₂O, that oxidizes sulfite ions to sulfateions, which is a well-known practice for fermentation toacetone/butanol/ethanol (ABE). Preferably, the residual SO₂ is reducedto less than about 100 ppm, 50 ppm, 25 ppm, 10 ppm, 5 ppm, or 1 ppm.

In some embodiments, the process further comprises recovering the ligninas a co-product. The sulfonated lignin may also be recovered as aco-product. In certain embodiments, the process further comprisescombusting or gasifying the sulfonated lignin, recovering sulfurcontained in the sulfonated lignin in a gas stream comprising reclaimedsulfur dioxide, and then recycling the reclaimed sulfur dioxide forreuse.

The process lignin separation step is for the separation of lignin fromthe hydrolysate and can be located before or after the final reactionstep and evaporation. If located after, then lignin will precipitatefrom the hydrolysate since alcohol has been removed in the evaporationstep. The remaining water-soluble lignosulfonates may be precipitated byconverting the hydrolysate to an alkaline condition (pH higher than 7)using, for example, an alkaline earth oxide, preferably calcium oxide(lime). The combined lignin and lignosulfonate precipitate may befiltered. The lignin and lignosulfonate filter cake may be dried as aco-product or burned or gasified for energy production. The hydrolysatefrom filtering may be recovered and sold as a concentrated sugarsolution product or further processed in a subsequent fermentation orother reaction step.

Native (non-sulfonated) lignin is hydrophobic, while lignosulfonates arehydrophilic. Hydrophilic lignosulfonates may have less propensity toclump, agglomerate, and stick to surfaces. Even lignosulfonates that doundergo some condensation and increase of molecular weight, will stillhave an HSO₃ group that will contribute some solubility (hydrophilic).

In some embodiments, the soluble lignin precipitates from thehydrolysate after solvent has been removed in the evaporation step. Insome embodiments, reactive lignosulfonates are selectively precipitatedfrom hydrolysate using excess lime (or other base, such as ammonia) inthe presence of aliphatic alcohol. In some embodiments, hydrated lime isused to precipitate lignosulfonates. In some embodiments, part of thelignin is precipitated in reactive form and the remaining lignin issulfonated in water-soluble form.

The process fermentation and distillation steps are intended for theproduction of fermentation products, such as alcohols or organic acids.After removal of cooking chemicals and lignin, and further treatment(oligomer hydrolysis), the hydrolysate contains mainly fermentablesugars in water solution from which any fermentation inhibitors havebeen preferably removed or neutralized. The hydrolysate is fermented toproduce dilute alcohol or organic acids, from 1 wt % to 20 wt %concentration. The dilute product is distilled or otherwise purified asis known in the art.

When alcohol is produced, such as ethanol, some of it may be used forcooking liquor makeup in the process cooking step. Also, in someembodiments, a distillation column stream, such as the bottoms, with orwithout evaporator condensate, may be reused to wash cellulose. In someembodiments, lime may be used to dehydrate product alcohol. Sideproducts may be removed and recovered from the hydrolysate. These sideproducts may be isolated by processing the vent from the final reactionstep and/or the condensate from the evaporation step. Side productsinclude furfural, hydroxymethyl furfural (HMF), methanol, acetic acid,and lignin-derived compounds, for example.

The glucose may be fermented to an alcohol, an organic acid, or anotherfermentation product. The glucose may be used as a sweetener orisomerized to enrich its fructose content. The glucose may be used toproduce baker's yeast. The glucose may be catalytically or thermallyconverted to various organic acids and other materials.

When hemicellulose is present in the starting biomass, all or a portionof the liquid phase contains hemicellulose sugars and soluble oligomers.It is preferred to remove most of the lignin from the liquid, asdescribed above, to produce a fermentation broth which will containwater, possibly some of the solvent for lignin, hemicellulose sugars,and various minor components from the digestion process. Thisfermentation broth can be used directly, combined with one or more otherfermentation streams, or further treated. Further treatment can includesugar concentration by evaporation; addition of glucose or other sugars(optionally as obtained from cellulose saccharification); addition ofvarious nutrients such as salts, vitamins, or trace elements; pHadjustment; and removal of fermentation inhibitors such as acetic acidand phenolic compounds. The choice of conditioning steps should bespecific to the target product(s) and microorganism(s) employed.

In some embodiments, hemicellulose sugars are not fermented but ratherare recovered and purified, stored, sold, or converted to a specialtyproduct. Xylose, for example, can be converted into xylitol.

A lignin product can be readily obtained from a liquid phase using oneor more of several methods. One simple technique is to evaporate off allliquid, resulting in a solid lignin-rich residue. This technique wouldbe especially advantageous if the solvent for lignin iswater-immiscible. Another method is to cause the lignin to precipitateout of solution. Some of the ways to precipitate the lignin include (1)removing the solvent for lignin from the liquid phase, but not thewater, such as by selectively evaporating the solvent from the liquidphase until the lignin is no longer soluble; (2) diluting the liquidphase with water until the lignin is no longer soluble; and (3)adjusting the temperature and/or pH of the liquid phase. Methods such ascentrifugation can then be utilized to capture the lignin. Yet anothertechnique for removing the lignin is continuous liquid-liquid extractionto selectively remove the lignin from the liquid phase, followed byremoval of the extraction solvent to recover relatively pure lignin.

Lignin produced in accordance with the invention can be used as a fuel.As a solid fuel, lignin is similar in energy content to coal. Lignin canact as an oxygenated component in liquid fuels, to enhance octane whilemeeting standards as a renewable fuel. The lignin produced herein canalso be used as polymeric material, and as a chemical precursor forproducing lignin derivatives. The sulfonated lignin may be sold as alignosulfonate product, or burned for fuel value.

The present invention also provides systems configured for carrying outthe disclosed processes, and compositions produced therefrom. Any streamgenerated by the disclosed processes may be partially or completedrecovered, purified or further treated, and/or marketed or sold.

Certain nanocellulose-containing products provide high transparency,good mechanical strength, and/or enhanced gas (e.g., O₂ or CO₂) barrierproperties, for example. Certain nanocellulose-containing productscontaining hydrophobic nanocellulose materials provided herein may beuseful as anti-wetting and anti-icing coatings, for example.

Due to the low mechanical energy input, nanocellulose-containingproducts provided herein may be characterized by fewer defects thatnormally result from intense mechanical treatment.

Some embodiments provide nanocellulose-containing products withapplications for sensors, catalysts, antimicrobial materials, currentcarrying and energy storage capabilities. Cellulose nanocrystals havethe capacity to assist in the synthesis of metallic and semiconductingnanoparticle chains.

Some embodiments provide composites containing nanocellulose and acarbon-containing material, such as (but not limited to) lignin,graphite, graphene, or carbon aerogels.

Cellulose nanocrystals may be coupled with the stabilizing properties ofsurfactants and exploited for the fabrication of nanoarchitectures ofvarious semiconducting materials.

The reactive surface of —OH side groups in nanocellulose facilitatesgrafting chemical species to achieve different surface properties.Surface functionalization allows the tailoring of particle surfacechemistry to facilitate self-assembly, controlled dispersion within awide range of matrix polymers, and control of both the particle-particleand particle-matrix bond strength. Composites may be transparent, havetensile strengths greater than cast iron, and have very low coefficientof thermal expansion. Potential applications include, but are notlimited to, barrier films, antimicrobial films, transparent films,flexible displays, reinforcing fillers for polymers, biomedicalimplants, pharmaceuticals, drug delivery, fibers and textiles, templatesfor electronic components, separation membranes, batteries,supercapacitors, electroactive polymers, and many others.

Other nanocellulose applications suitable to the present inventioninclude reinforced polymers, high-strength spun fibers and textiles,advanced composite materials, films for barrier and other properties,additives for coatings, paints, lacquers and adhesives, switchableoptical devices, pharmaceuticals and drug delivery systems, bonereplacement and tooth repair, improved paper, packaging and buildingproducts, additives for foods and cosmetics, catalysts, and hydrogels.

Aerospace and transportation composites may benefit from highcrystallinity. Automotive applications include nanocellulose compositeswith polypropylene, polyamide (e.g. Nylons), or polyesters (e.g. PBT).

Nanocellulose materials provided herein are suitable asstrength-enhancing additives for renewable and biodegradable composites.The cellulosic nanofibrillar structures may function as a binder betweentwo organic phases for improved fracture toughness and prevention ofcrack formation for application in packaging, construction materials,appliances, and renewable fibers.

Nanocellulose materials provided herein are suitable as transparent anddimensional stable strength-enhancing additives and substrates forapplication in flexible displays, flexible circuits, printableelectronics, and flexible solar panels. Nanocellulose is incorporatedinto the substrate-sheets are formed by vacuum filtration, dried underpressure and calandered, for example. In a sheet structure,nanocellulose acts as a glue between the filler aggregates. The formedcalandered sheets are smooth and flexible.

Nanocellulose materials provided herein are suitable for composite andcement additives allowing for crack reduction and increased toughnessand strength. Foamed, cellular nanocellulose-concrete hybrid materialsallow for lightweight structures with increased crack reduction andstrength.

Strength enhancement with nanocellulose increases both the binding areaand binding strength for application in high strength, high bulk, highfiller content paper and board with enhanced moisture and oxygen barrierproperties. The pulp and paper industry in particular may benefit fromnanocellulose materials provided herein.

Nanofibrillated cellulose nanopaper has a higher density and highertensile mechanical properties than conventional paper. It can also beoptically transparent and flexible, with low thermal expansion andexcellent oxygen barrier characteristics. The functionality of thenanopaper can be further broadened by incorporating other entities suchas carbon nanotubes, nanoclay or a conductive polymer coating.

Porous nanocellulose may be used for cellular bioplastics, insulationand plastics and bioactive membranes and filters. Highly porousnanocellulose materials are generally of high interest in themanufacturing of filtration media as well as for biomedicalapplications, e.g., in dialysis membranes.

Nanocellulose materials provided herein are suitable as coatingmaterials as they are expected to have a high oxygen barrier andaffinity to wood fibers for application in food packaging and printingpapers.

Nanocellulose materials provided herein are suitable as additives toimprove the durability of paint, protecting paints and varnishes fromattrition caused by UV radiation.

Nanocellulose materials provided herein are suitable as thickeningagents in food and cosmetics products. Nanocellulose can be used asthixotropic, biodegradable, dimensionally stable thickener (stableagainst temperature and salt addition). Nanocellulose materials providedherein are suitable as a Pickering stabilizer for emulsions and particlestabilized foam.

The large surface area of these nanocellulose materials in combinationwith their biodegradability makes them attractive materials for highlyporous, mechanically stable aerogels. Nanocellulose aerogels display aporosity of 95% or higher, and they are ductile and flexible.

Drilling fluids are fluids used in drilling in the natural gas and oilindustries, as well as other industries that use large drillingequipment. The drilling fluids are used to lubricate, providehydrostatic pressure, and to keep the drill cool, and the hole as cleanas possible of drill cuttings. Nanocellulose materials provided hereinare suitable as additives to these drilling fluids.

In this detailed description, reference has been made to multipleembodiments of the invention and non-limiting examples relating to howthe invention can be understood and practiced. Other embodiments that donot provide all of the features and advantages set forth herein may beutilized, without departing from the spirit and scope of the presentinvention. This invention incorporates routine experimentation andoptimization of the methods and systems described herein. Suchmodifications and variations are considered to be within the scope ofthe invention defined by the claims.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain of the steps may be performedconcurrently in a parallel process when possible, as well as performedsequentially.

Therefore, to the extent there are variations of the invention, whichare within the spirit of the disclosure or equivalent to the inventionsfound in the appended claims, it is the intent that this patent willcover those variations as well. The present invention shall only belimited by what is claimed.

What is claimed is:
 1. A method of reinforcing cellulose fibers, saidmethod comprising: (a) providing cellulose fibers derived fromhardwoods, agricultural residues, or a combination thereof; (b)providing a source of nanocellulose comprising cellulose nanofibrilsand/or cellulose nanocrystals; and (c) reinforcing said cellulose fiberswith said nanocellulose to increase strength of said cellulose fibers.2. The method of claim 1, wherein said nanocellulose is derived from abiomass source selected from the group consisting of hardwoods,softwoods, agricultural residues, and combinations thereof.
 3. Themethod of claim 1, wherein said nanocellulose is obtained fromfractionating biomass in the presence of an acid, a solvent for lignin,and water, to generate cellulose-rich solids and a liquid phase; andthen mechanically refining said cellulose-rich solids to generate saidnanocellulose.
 4. The method of claim 3, wherein said acid is sulfurdioxide and said solvent is ethanol.
 5. The method of claim 1, saidmethod further comprising producing a single-fiber product from saidcellulose fibers.
 6. The method of claim 1, said method furthercomprising producing a composite from said cellulose fibers.
 7. Acomposition comprising nanocellulose-reinforced cellulose fibers,wherein said composition is produced by a method comprising: (a)providing cellulose fibers derived from hardwoods, agriculturalresidues, or a combination thereof; (b) providing a source ofnanocellulose comprising cellulose nanofibrils and/or cellulosenanocrystals; and (c) reinforcing said cellulose fibers with saidnanocellulose to increase strength of said cellulose fibers.
 8. Thecomposition of claim 7, wherein said nanocellulose is derived from abiomass source selected from the group consisting of hardwoods,softwoods, agricultural residues, and combinations thereof.
 9. Thecomposition of claim 7, wherein said nanocellulose is obtained fromfractionating biomass in the presence of an acid, a solvent for lignin,and water, to generate cellulose-rich solids and a liquid phase; andthen mechanically refining said cellulose-rich solids to generate saidnanocellulose.
 10. The composition of claim 9, wherein said acid issulfur dioxide and said solvent is ethanol.
 11. The composition of claim7, wherein said cellulose fibers are present in a single-fiber product.12. The composition of claim 7, wherein said cellulose fibers arepresent in a composite.